Portion of a humidifier tub



FIG. 1 is a front perspective view of a portion of a humidifier tubaccording to our design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a right side view thereof; and,

FIG. 6 is a left side view thereof.

Where included, broken lines showing environment or structure are forillustrative purposes only and form no part of the claimed design. Whereincluded, dotted lines represent the border between claimed andnon-claimed subject matter and form no part of the claimed design.

The ornamental design for a portion of a humidifier tub, as shown anddescribed.